This invention relates to heat pipes and, more particularly, to heat pipes having an integral metallic bond between the porous wick and the metal skin or case.
Typically, a heat pipe is comprised of a hermetic enclosure or case containing a porous capillary structure normally called a wick, a void volume, and a working fluid. The wick contains the liquid phase of the working fluid. The void volume of the container not occupied by the wick contains saturated working fluid vapor.
Heat pipes transfer heat internally by mass transfer. The working fluid vaporizes wherever heat is added and then flows to wherever heat is removed. The working fluid condenses where heat is removed and this liquid is returned to where heat is added by capillary action in the wick. Heat is added in the section of the heat pipe normally referred to as the evaporator and heat is released in the section of the heat pipe normally referred to as the condenser.
A large temperature drop encountered in heat pipes occurs in both the evaporator and condenser sections where heat is conducted through the enclosure or case, the enclosure-to-wick interface, and through the wick and working fluid. Thermal resistance at the enclosure-to-wick interface is a significant portion of the overall heat pipe temperature drop.
Prior art methods of heat pipe manufacture begin with pre-formed, i.e. extruded or machined, enclosure and may be more than one piece. Great care must be used to place the wick material at desired locations. Means must be provided to tightly press the wick pieces against the enclosure surfaces (as by springs, welding, diffusion bonding, etc.) in order to minimize the enclosure-to-wick thermal resistance. For the enclosures made of several pieces, normally done to provide access during wick placement, the final hermetic seals are typically accomplished by welding, brazing, or soldering the enclosure pieces together. This technique is susceptible to leakage at the joints which, of course, leads to heat pipe failure.
Prior art heat pipes are typically expensive to manufacture due to labor intensive wick placement and retention, are susceptible to failure due to leakage at the various joints in the enclosure, and can exhibit degraded performance because of high enclosure-to-wick thermal resistance.
It is an object of this invention to produce a hermetically sealed heat pipe enclosure having a metallurgical bond to the internally contained wick to insure low enclosure-to-wick thermal resistance.
It is a further object of this invention to produce an inexpensive heat pipe without joints or seams, except at the point where provision is made for adding the working fluid, usually a tube, in order to reduce susceptability to leaks.